Introduction
Cytokine response patterns play an important role in inflammatory, infectious and autoimmune diseases, in both humans and mammals. Tumor necrosis factor-alpha (TNF-.alpha.), also termed "Cachectin", is a naturally occurring cytokine with many functions in the human immune system. It is thought to medicate both protective and detrimental manifestations of the inflammatory response. Over-expression of TNF-.alpha. has been linked to inflammation and to higher rates of apoptosis, resulting in untoward clinical manifestations.
TNF-.alpha. in eye disorders
A coherent view of the role of TNF-.alpha. in inflammatory eye disease is emerging as a result of studies both in man and in experimental animals. TNF-.alpha. is found in ocular tissues obtained from patients with intra-ocular inflammation (uveitis). Studies have shown that TNF-.alpha. induces uveitis in the rabbit eye (Kulkarni P S and Srinivasin B D, Exp Eye Res 1988; 46(4):631-633). Common complications of ocular inflammation such as glaucoma, keratic precipitates, retinal (macular) oedema and neovascularization may be mediated by TNF-.alpha..
The blood-retinal barrier (BRB), which is formed by the retinal vascular endothelium and the retinal pigment epithelium, is responsible for controlling the passage of cells and molecules into the neuroretina. During ocular inflammatory diseases, however, this selective control is altered due to changes in BRB function such as increased permeability and leukocyte recruitment. The causative factors leading to barrier breakdown are not entirely understood, although cytokines have recently been implicated. In vivo studies, using a rat model revealed that elevated levels of TNF-.alpha. cause an in crease in the BRB permeability, thus inducing the infiltration of inflammatory cells (Bamforth SD et al, Acta Neuropathol (Berl) 1996; 91(6):624-632).
Experimental autoimmune uveoretinitis (EAU) serves as a model for several immune-mediated diseases that affect the eye in humans and it has been postulated that TNF-.alpha. has an important pro-inflammatory role in EAU and possibly in human uveitis. It has been shown that neutralization of systemic TNF-.alpha. ameliorates EAU (Sartani G et al, Invest Ophthalmol Vis Sci 1996; 37(11):2211-2218). In vitro studies have also demonstrated that conjunctival epithelial cells secreted the pro-inflammatory cytokines, TNF-.alpha. in response to stimuli, suggesting that these cells may contribute to the pathogenesis of human ocular diseases by production of these pro-inflammatory cytokines (Gamache D A et al, Ocul Immunol Inflamm 1997; 5(2): 117-128).
Ultraviolet (UV) irradiation exposure represents a significant environmental and occupational hazard that can cause acute and chronic inflammatory changes in the exposed cornea, and laboratory studies have shown that acute UV exposure leads to a significant increase in the production of TNF-.alpha. (Kennedy M, et al, Invest Ophthalmol Vis Sci 1997; 38(12):2483-2491).
TNF-.alpha. has the capacity to mediate neuronal or axonal injury, leading to optic neuropathy (Madigan MC et al, Neurol Res 1996; 18(2):176-184). Corneal allograft rejection culminates in a series of interactions between different classes of antigen presenting cells, cytokines and leukocytes. TNF-.alpha. was recently reported to be elevated in acute rejection of solid organ transplants (Pleyer U et al, Ocul Immunol Inflamm 1997; 5(3): 149-155). Studies demonstrate that gamma-Interferon and TNF-.alpha. exert an enhancing effect on man corneal epithelial (HCE) cells and on the adhesion of lymphocytes to HCE cells, directly or via enhancement of ICAM-1 expression (Iwata M et al, Curr Eye Res 1997; 16(8):751-760).
TNF-.alpha. in disorders of the oral cavity
TNF-.alpha. in eye disorders
TNF-.alpha. is involved in the formation and exacerbation of oral cavity disorders, as revealed by human studies as well as in experimental animals. Recurrent Aphthous Ulcers (RAU's), commonly known as canker sores, are benign open sores in the mouth, which appear as painful white or yellow sores (ulcers) surrounded by a bright red area. The cause is unknown. Much evidence suggests that RAU is an immunologically mediated disease. Parallels have been drawn between the immunopathologic characteristics of aphthous lesions with local increases in the ratio of CD4: CD8 infiltrating T-lymphocytes and induction of class II major histocompatibility molecules on keratinocytes and epithelial cells. The latter observation suggests an active cytokine response. Recent studies indicate a possible etiologic role for locally produced TNF-.alpha. in RAU. Significantly greater amounts of TNF-.alpha. were released from unstimulated monocyte- enriched and monocytedepleted leukocyte fractions in active RAU compared with those from healthy control donors, suggesting that this cytokine may be associated with RAU (Taylor L. J.; Bagg J., Walker D. M. and Peters T. J., J. Oral Pathol. Med., 1992; 21(1):21-25). Further studies have demonstrated that TNF-.alpha. production is increased in peripheral blood lymphocytes of healthy patients with RAU (MacPhail L A. and Greenspan J. S., Oral Dis 1997; 3 Suppl 1:S190-S193).
Periodontal disease is the most frequent cause of tooth loss in humans and is the most prevalent disease associated with bone loss, including osteoporosis. Bacteria that colonize the tooth surface, leading to inflammation and bone resorption initiate periodontal destruction. In vivo studies have shown that the pathologic process of periodontitis is due to TNF-.alpha. activity (Assuma R. et al, J Immunol 1998; 160(1):403-409). Autoimmune disorders of the oral cavity, e.g., oral lichen have also been associated with elevated levels of TNF-.alpha. (Zahran F. M., Egypt Dent J 1995; 41(4): 1363-1366).
In conclusion, it is conceivable that various ophthalmic and mucosal disorders are associated with overexpression of pro-inflammatory cytokines, and that attenuation of those cytokines may be beneficial in the treatment of such disorders.
Current uses of anti-TNF-.alpha. agents
Various anti-TNF-.alpha. agents have been proposed as therapeutic modalities for inflammatory and autoimmune disorders. Pentoxifylline has been claimed to affect TNF-.alpha. related disorders (U.S. Pat. Nos. 5,370,870; 5,502,066; 5,585,380; 5,641,783; 5,643,875; 5,672,622; 5,730,975). Oral administration of pentoxifylline has been shown experimentally to exert a beneficial effect on thyroid associated ophthalmopathy (TAO) and the response was correlated with reduction of TNF-.alpha. levels (Balazs C et al, J Clin Endocrinol Metab 1997; 82(6):1999-2002). However, none of the above mentioned patents and publications relates to the topical use of pentoxifylline in eye disorders. Other xantliines, e.g., propentofylline, also possess anti-TNF-.alpha. properties, but none has been reported to be used topically on the mucosal tissues of the eye and the oral cavity.
Thalidomide is another known inhibitor of TNF-.alpha. has been demonstrated effective in TNF-related disorders, and was approved by the FDA for the treatment of RAU in patients with AIDS or cancer. Thalidomide is given orally to patient, in doses of 100 mg, four times per day, thus exposing them to known adverse effects of this drug. U.S. Pat. Nos. 5,385,901; 5,502,066; 5,635,517 and 5,712,291 claim the use of thalidomide in TNF-.alpha.--related disorders, however, none of said patents relates to a topical application of thalidomide or to topical delivery systems for this agent onto mucosal tissues.
Topical delivery of anti- TNF-.alpha. agents
Direct topical application of pharmacological agents onto mucosal tissues the eye and the mouse cavity has not been reported in the prior art. Due to the facile clearance of those agents, via washing by tears and mouth fluids, specific formulations, designed to prolong the availability of the therapeutic product on the surface and to enable sustained release of the active ingredient have been developed. Mucoadhesion is generally understood as the ability of a biological or synthetic material to "stick" to mucous membrane, resulting in adherence of the material to the tissue for protracted period of time. Mucoadhesive materials are generally high molecular weight polymers. These polymers entangled into the mucin layer forming a complex layer of polymers and mucin. The presence of different functional groups on the polymeric backbone is important as well. It is known that hydrogen bonding plays an important roll in adhesion (Morrtazavi, SA, Intl J Pharm 1995;124(2):173).